1. Field of the Invention
The present invention generally relates to a paper size detection device, and more particularly to a paper size detection device having a simple structure and a lower manufacture cost, and a detection method thereof.
2. The Related Art
Referring to FIG. 12, a current paper size detection device 900 adapted for being mounted to a paper platform 902 includes a first light sensor 904, a first switch 906, a second light sensor 908, a second switch 910, a third light sensor 912 and a third switch 914. The first light sensor 904, the second light sensor 908 and the third light sensor 912 are disposed in the paper platform 902. The first switch 906, the second switch 910 and the third switch 914 are separately disposed to the paper platform 902 with top ends thereof projecting beyond a top surface of the paper platform 902 at intervals, and tail ends thereof corresponding to the first light sensor 904, the second light sensor 908 and the third light sensor 912, separately.
Each of the first light sensor 904, the second light sensor 908 and the third light sensor 912 has a light emitting portion 916 and a light receiving portion 918 parallel to each other. The light emitting portion 916 and the light receiving portion 918 have a same operation principle in the first light sensor 904, the second light sensor 908 and the third light sensor 912. Now take the first light sensor 904 for example to explain, when there are no obstacles disposed between the light emitting portion 916 and the light receiving portion 918, light beams emitted by the light emitting portion 916 are able to be received by the light receiving portion 918, and then the first light sensor 904 outputs a high level signal. When the tail end of the first switch 906 moves to a middle position between the light emitting portion 916 and the light receiving portion 918, the light beams emitted by the light emitting portion 916 are blocked by the tail end of the first switch 906 that results in the light receiving portion 918 has no way to receive the light beams emitted by the light emitting portion 916, and then the first light sensor 904 outputs a low level signal.
When the paper size detection device 900 is operated, operations of the first light sensor 904, the second light sensor 908, the third light sensor 912, the first switch 906, the second switch 910 and the third switch 914 are described as follows. When there is no paper put on the paper platform 902, the top ends of the first switch 906, the second switch 910 and the third switch 914 project beyond the top of the paper platform 902, and the tail ends of the first switch 906, the second switch 910 and the third switch 914 are disposed out of the first light sensor 904, the second light sensor 908, the third light sensor 912, separately, thus, the first light sensor 904, the second light sensor 908 and the third light sensor 912 separately output the high level signal. So, when the first light sensor 904, the second light sensor 908 and the third light sensor 912 separately output the high level signal, it can be judged that there is no paper put on the paper platform 902.
When there is a small-sized paper put on the paper platform 902, the small-sized paper can just press against the top end of the first switch 906, and then brings along the tail end of the first switch 906 to move into the first light sensor 904 and obstruct the first light sensor 904, thus, the signal outputted by the first light sensor 904 turns from high level to low level. So, when the first light sensor 904 outputs the low level signal, and the second light sensor 908 and the third light sensor 912 respectively output the high level signal, it can be judged that there is the small-sized paper put on the paper platform 902.
When there is a middle-sized paper put on the paper platform 902, the middle-sized paper can just press against the top ends of the first switch 906 and the second switch 910, and then brings along the tail ends of the first switch 906 and the second switch 910 to respectively move into the first light sensor 904 and the second light sensor 908 and obstruct the first light sensor 904 and the second light sensor 908, thus, the signal respectively outputted by the first light sensor 904 and the second light sensor 908 turns from high level to low level. So, when the first light sensor 904 and the second light sensor 908 respectively output the low level signal, and the third light sensor 912 outputs the high level signal, it can be judged that there is the middle-sized paper put on the paper platform 902.
When there is a large-sized paper put on the paper platform 902, the large-sized paper can just press against the top ends of the first switch 906, the second switch 910 and the third switch 914, and then brings along the tail ends of the first switch 906, the second switch 910 and the third switch 914 to separately move into the first light sensor 904, the second light sensor 908 and the third light sensor 912, and obstruct the first light sensor 904, the second light sensor 908 and the third light sensor 912, thus, the signal respectively outputted by the first light sensor 904, the second light sensor 908 and the third light sensor 912 turns from high level to low level. So, when the first light sensor 904, the second light sensor 908 and the third light sensor 912 separately output the low level signal, it can be judged that there is the large-sized paper put on the paper platform 902.
However, the paper size detection device 900 needs the above-mentioned three light sensors to cooperate with the above-mentioned three switches to be able to detect the above-mentioned three sizes of the papers. Therefore, the aforesaid setting structure of the paper size detection device 900 needs more elements that results in the paper size detection device 900 having a complex structure and a higher manufacture cost.